The ribosome turns a nucleic acid sequence into a protein sequence. Its small subunit checks each codon against the anticodon of an incoming tRNA. Its large subunit joins the new amino acid to the growing chain, using RNA alone as the catalyst. The two subunits then rotate against each other and the mRNA advances by one codon.
12-17 amino acids per second
Elongation rate in E. coli
1012 at slow growth and 17 at fast growth, measured by pulse labelling.
2-20 amino acids per second
Elongation rate across systems
7Range quoted for sequential selection and translocation cycles.
10^-3 to 10^-5
Error per elongation step, held over thousands of cycles.
10^-3 to 10^-4
Missense error rate per codon
11Rates differ widely between codons, and depend on competition between tRNAs.
none within ~18 A
Protein near the new peptide bond
2Only 23S rRNA residues contact the substrate analogues, so the catalyst is RNA.
1542 / 2904 / 120 nucleotides
16S, 23S and 5S rRNA of E. coli, from the entity sequences of PDB 7K00.
~20 small, ~30 large
Counted as modelled in PDB 7K00 for E. coli.
3
A, P and E sites. A tRNA passes through them in that order.